Silole‐containing polymers for high‐efficiency polymer solar cells

Silole‐containing conjugated polymers ( P1 and P2 ) carrying methyl and octyl substituents, respectively, on the silicon atom were synthesized by Suzuki polycondensation. They show strong absorption in the region of 300–700 nm with a band gap of about 1.9 eV. The two silole‐containing conjugated polymers were used to fabricate polymer solar cells by blending with PC₆₁BM and PC₇₁BM as the active layer. The best performance of photovoltaic devices based on P1 /PC₇₁BM active layer exhibited power conversion efficiency (PCE) of 2.72%, whereas that of the photovoltaic cells fabricated with P2 /PC₇₁BM exhibited PCE of 5.08%. 1,8‐Diiodooctane was used as an additive to adjust the morphology of the active layer during the device optimization. PCE of devices based on P2 /PC₇₁BM was further improved to 6.05% when a TiO_x layer was used as a hole‐blocking layer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Effect of side‐chain positions on morphology and photovoltaic properties of phenazine‐based donor–acceptor copolymers

Two phenazine donor–acceptor‐conjugated copolymers (P1 and P2) with the same polymer backbone but different anchoring positions of alkoxy chain on the phenazine unit were investigated to identify the effect of changing the position of alkoxy chains on their optical, electrochemical, blend film morphology, and photovoltaic properties. Although the optical absorption and frontier orbital energy levels were insensitive to the position of alkoxy chains, the film morphologies and photovoltaic performances changed significantly. P1/PC₇₁BM blend film showed the formation of phase separation with large coarse aggregates, whereas P2/PC₇₁BM blend film was homogeneous and smooth. Accordingly, power conversion efficiency (PCE) of photovoltaic devices increased from 1.50% for P1 to 2.54% for P2. In addition, the PCE of the polymer solar cell based on P2/PC₇₁BM blend film could be further improved to 3.49% by using solvent vapor annealing treatment. These results clearly revealed that tuning the side‐chain position could be an effective way to adjust the morphology of the active layer and the efficiency of the photovoltaic device. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2910–2918     

Morphological study of an intrinsically stretchable photovoltaic bulk heterojunction

Thin‐film polymer solar cell consisting of [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) and poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]] (PTB7) demonstrates elastic stretchability with the aid of a high boiling point additive, 1,8‐diiodooctane (DIO). The usage of DIO not only helps to form uniformly distributed nanocrystalline grains, but may also create free volumes between the nano‐grains that allow for relative sliding between the nano‐grains. The relative sliding can accommodate large external deformation. Large dichroic ratios of the optical absorption of both PC₇₁BM and PTB7 were observed under large‐strain deformation, indicating reorientation of the nanocrystalline PC₇₁BM and PTB7 polymer chains along stretching direction. The dichroic ratio decreases to nearly 1.0 as the blend was relaxed to 0% strain. Therefore, the nanometer‐size grain blending morphology provides an approach to impart stretchability to organic semiconductors that are otherwise un‐stretchable. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 814–820     

Tailorable PC71BM Isomers: Using the Most Prevalent Electron Acceptor to Obtain High‐Performance Polymer Solar Cells

Despite being widely used as electron acceptor in polymer solar cells, commercially available PC₇₁BM (phenyl‐C₇₁‐butyric acid methyl ester) usually has a “random” composition of mixed regioisomers or stereoisomers. Here PC₇₁BM has been isolated into three typical isomers, α‐, β₁‐ and β₂‐PC₇₁BM, to establish the isomer‐dependent photovoltaic performance on changing the ternary composition of α‐, β₁‐ and β₂‐PC₇₁BM. Mixing the isomers in a ratio of α/β₁/β₂=8:1:1 resulted in the best power conversion efficiency (PCE) of 7.67 % for the polymer solar cells with PTB7:PC₇₁BM as photoactive layer (PTB7=poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]]). The three typical PC₇₁BM isomers, even though sharing similar LUMO energy levels and light absorption, render starkly different photovoltaic performances with average‐performing PCE of 1.28–7.44 % due to diverse self‐aggregation of individual or mixed PC₇₁BM isomers in the otherwise same polymer solar cells.     

Impact of 1,8-diiodooctane on the morphology of organic photovoltaic (OPV) devices – A Small Angle Neutron Scattering (SANS) study

The impact of the additive 1,8-diiodooctane on the morphology of bulk-heterojunction solar cells based on the systems P3HT:PC₇₁BM, PTB7:PC₇₁BM and PTB7-Th:PC₇₁BM is studied using a combination of Small Angle Neutron Scattering (SANS) and Atomic Force Microscopy (AFM). The results clearly show that while in the P3HT:PC₇₁BM system, the additive DIO promotes a slight coarsening of the phase domains (type I additive), in the systems PTB7:PC₇₁BM and PTB7-Th:PC₇₁BM, DIO promotes a large decrease in the size of the phase domains (type II additive). SANS is demonstrated as being particularly useful at detecting the minor morphological changes observed in the P3HT:PC₇₁BM system, which can be hardly seen in AFM. This work illustrates how SANS complements AFM and both techniques when used together provide a deeper insight into the nanoscale structure in thin organic photovoltaic (OPV) device films.     

Synthesis of phenanthro[1,10,9,8‐cdefg]carbazole‐based conjugated polymers for organic solar cell applications

Low bandgap polymers with dithienylquinoxaline moieties based on 6H‐phenanthro[1,10,9,8‐cdefg]carbazole were synthesized via the Suzuki coupling reaction. Alkoxy groups were substituted at two different positions on the phenyl groups of the quinoxaline units of these polymers: in the para‐position (PPQP) and in the meta‐position (PPQM). The two polymers showed similar physical properties: broad absorption in the range of 400–700 nm, optical bandgaps of ～1.8 eV, and the appropriate frontier orbital energy levels for efficient charge transfer/separation at polymer/PC₇₁BM interfaces. However, the PPQM solar cell achieved a higher PCE due to its higher J_sc. Our investigation of the morphologies of the polymer:PC₇₁BM blend films and theoretical calculations of the molecular conformations of the polymer chains showed that the polymer with the meta‐positioned alkoxy group has better miscibility with PC₇₁BM than the polymer with the para‐positioned alkoxy group because the dihedral angle of its phenyl group with respect to the quinoxaline unit is higher. This higher miscibility resulted in a polymer:PC₇₁BM blend film with a better morphology and thus in a higher PCE. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 796–803     

Copolymers of fluorene and thiophene with conjugated side chain for polymer solar cells: Effect of pendant acceptors

Two copolymers of fluorene and thiophene with conjugated side‐chain pending acceptor end group of cyanoacetate ( P2 ) and malononitrile ( P3 ) were synthesized. Both polymers exhibit good thermal stability and low highest occupied molecular orbital level (?5.5 eV). In comparison with P2 , P3 exhibits stronger UV–vis absorption and higher hole mobility. Polymer solar cells based on P3 :PC₇₁BM exhibits a power conversion efficiency of 1.33% under AM 1.5, 100 mW/cm², which is three times of that based on P2 :PC₇₁BM. The higher efficiency is attributed to better absorption, higher hole mobility, and the reduced phase separation scale in P3 :PC₇₁BM blend. The aggregate domain size in P3 :PC₇₁BM blend is 50 nm, much smaller than that in P2 :PC₇₁BM blend (200 nm). Tiny difference in the end groups on side chains of P2 and P3 leads to great difference in phase separation scale, charge transport, and efficiency of their photovoltaic devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

DR3TBDTT Based Ternary Blends Containing Conjugated Polymers: Crystallization Determines Morphology and Performance

How the conjugated polymers affect the crystallization of DR3TBDTT, in addition to the corresponding morphology and performance, is not well understood. In this work, the weakly crystalline polymer PTB7‐Th and highly crystalline polymers of PCDTBT and P3HT were incorporated into DR3TBDTT:PC₇₁BM system to investigate the variation of crystallization, morphology and performance. It is demonstrated that PTB7‐Th is the most effective additive to improve the PCE value of DR3TBDTT:PC₇₁BM to 5.7%, showing the nucleating agent reducing the crystallization correlation length (CCL) value of DR3TBDTT from 18.7 nm to 17.0 nm, in addition to the optimized morphology. In contrast, the PCDTBT and P3HT could induce the crystallization of DR3TBDTT, leading to much higher CCL value as well as obvious phase separation. Despite of energy level alignment, the crystallization of DR3TBDTT influenced by polymers determines the corresponding morphology of active layers and photovoltaic performance.     

Effects of additives on the morphology of solution phase aggregates formed by active layer components of high-efficiency organic solar cells

Processing additives are used in organic photovoltaic systems to optimize the active layer film morphology. However, the actual mechanism is not well understood. Using X-ray scattering techniques, we analyze the effects of an additive diiodooctane (DIO) on the aggregation of a high-efficiency donor polymer PTB7 and an acceptor molecule PC(71)BM under solar cell processing conditions. We conclude that DIO selectively dissolves PC(71)BM aggregates, allowing their intercalation into PTB7 domains, thereby optimizing both the domain size and the PTB7-PC(71)BM interface.     

The phase behavior of a polymer‐fullerene bulk heterojunction system that contains bimolecular crystals

Polymer:fullerene blends have been widely studied as an inexpensive alternative to traditional silicon solar cells. Some polymer:fullerene blends, such as blends of poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene (pBTTT) with phenyl‐c71‐butyric acid methyl ester (PC₇₁BM), form bimolecular crystals due to fullerene intercalation between the polymer side chains. Here we present the determination of the eutectic pBTTT:PC₇₁BM phase diagram using differential scanning calorimetry (DSC) and two‐dimensional grazing incidence X‐ray scattering (2D GIXS) with in‐situ thermal annealing. The phase diagram explains why the most efficient pBTTT:PC₇₁BM solar cells have 75–80 wt % PC₇₁BM since these blends lie in the center of the only room‐temperature phase region containing both electron‐conducting (PC₇₁BM) and hole‐conducting (bimolecular crystal) phases. We show that intercalation can be suppressed in 50:50 pBTTT:PC₇₁BM blends by using rapid thermal annealing to heat the blends above the eutectic temperature, which forces PC₇₁BM out of the bimolecular crystal, followed by quick cooling to kinetically trap the pure PC₇₁BM phase. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Synthesis of D-A copolymers based on thiadiazole and thiazolothiazole acceptor units and their applications in ternary polymer solar cells

We have designed and synthesized two wide bandgap new donor-acceptor (D-A) copolymers consisting of the same alkylthiazole-substituted benzo[1,2-b;4,5-b′]dithiophene (BDTTz) donor unit and but different acceptor units, i.e., thiazolo[5,4-d]thiazole (TT_Z) ( P122 ) and 1,3,-4 thiadiazole (TDz) ( P123 ) and investigated their optical and electrochemical properties. We have employed these copolymers as donor and fullerene (PC ₇₁ BM) and narrow bandgap non-fullerene (Y6) as acceptor, to fabricate binary and ternary bulk heterojunction polymer solar cells (PSCs). The overall power conversion efficiency (PCE) of optimized binary bulk heterojunction PSCs based on P122 :Y6 and P123 :Y6 is 12.60% and 13.16%, respectively. The higher PCE for PSCs based on P123 than P122 counterparts may be associated with the broader absorption profile of the P123 and more charge carrier mobilities than that for the P122 active layer. With the incorporation of small amount of PC₇₁BM into either P122 :Y6 or P123 :Y6 binary blend, the corresponding ternary PSCs showed an overall PCE of 14.89% and 15.52%, respectively, which is higher than the binary counterparts using either Y6 or PC₇₁BM as acceptor. Incorporating the PC₇₁BM in the binary host blend increases the absorption in the 300–500 nm wavelength region, generating more excitons in the active ternary layer and helping to dissociate the excitons into free charge carriers more effectively. The more appropriate nanoscale phase separation in the active ternary layer than the binary counterpart may be one of the reasons for higher PCE.     

Effect of Fluorination on the Photovoltaic Properties of Medium Bandgap Polymers for Polymer Solar Cells

Fluorination of conjugated polymers is one of the effective strategies to tune the molecular energy levels and morphology for high efficient polymer solar cells (PSCs). Herein, two novel donor‐acceptor conjugated polymers, PffBT and PBT, based on bis(3,5‐bis(hexyloxy)phenyl)benzo[1,2‐ b:4,5‐b']dithiophene and benzo[c][1,2,5]thiadiazole (BT) with or without fluorination, respectively, were synthesized, and their photovoltaic properties were compared. The polymer PffBT based on fluorinated BT showed lower frontier energy levels, improved polymer ordering, and a well‐developed fibril structure in the blend with PC₇₁BM. As a result, the PSCs based on PffBT/PC₇₁BM exhibit a superior power conversion efficiency (PCE) of 8.6% versus 4.4% for PBT‐based devices, due to a high space charge limit current (SCLC) hole mobility, mixed orientation of polymer crystals in the active layer, and low bimolecular recombination.     

Aqueous solution-processed NiOx anode buffer layers applicable for polymer solar cells

A green and facile method has been developed for the room temperature and aqueous solution preparation of NiO_x film as anode buffer layers for polymer solar cells (PSCs). The NiO_x buffer layer is prepared simply by spin-coating nickel acetylacetonate precursor-based aqueous solution onto ITO substrate at room temperature in air. UV-ozone post-treatment promotes the formation of dipolar NiOOH species on the film surface, resulting in the anode buffer layer with suitable work function. PSCs have been fabricated with the device structure of ITO/NiO_x/photoactive layer/PFN/Al. The power conversion efficiencies of the PSCs based on PTB7:PC₇₁BM blends (8.43%) and P3HT:PC₇₁BM blends (3.04%) with NiO_x anode buffer layer are comparable to those with the commonly used PEDOT:PSS anode buffer layer. In addition, the devices made with NiO_x buffer layer exhibit much better air stability than those with PEDOT:PSS. These results indicate that the water solution processed NiO_x film at room temperature in air is a promising anode buffer layer for efficient and stable PSCs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 747–753     

Development of a new conjugated polymer containing dialkoxynaphthalene for efficient polymer solar cells and organic thin film transistors

A new semiconducting polymer, poly((5,5‐E‐α‐((2‐thienyl)methylene)‐2‐thiopheneacetonitrile)‐alt‐2,6‐[(1,5‐didecyloxy)naphthalene])) (PBTADN), an alternating copolymer of 2,3‐bis‐(thiophene‐2‐yl)‐acrylronitrile and didecyloxy naphthalene, is synthesized and used as an active material for organic thin film transistors (OTFTs) and organic solar cells. The incorporation of 2,3‐bis‐(thiophene‐2‐yl)‐acrylronitrile as an electron deficient group and didecyloxy naphthalene as an electron rich group resulted in a relatively low bandgap, high charge carrier mobility, and finally good photovoltaic performances of PBTADN solar cells. Because of the excellent miscibility of PBTADN and PC₇₁BM, as confirmed by Grazing Incident X‐ray Scattering (GIXS) measurements and Transmission Electron Microscopy (TEM), homogeneous film morphology was achieved. The maximum power conversion efficiency of the PBTADN:PC₇₁BM solar cell reached 2.9% with a V_oc of 0.88 V, a short circuit current density (J_sc) of 5.6 mA/cm², and a fill factor of 59.1%. The solution processed thin film transistor with PBTADN revealed a highest saturation mobility of 0.025 cm²/Vs with an on/off ratio of 10⁴. The molecular weight dependence of the morphology, charge carrier mobility, and finally the photovoltaic performances were also studied and it was found that high molecular weight PBTADN has better self assembly characteristics, showing enhanced performance. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Thiazolothiazole‐containing polythiophenes with low HOMO level and high hole mobility for polymer solar cells

Two regiochemically defined polythiophenes containing thiazolothiazole acceptor unit were synthesized by palladium(0)‐catalyzed Stille coupling reaction. The thermal, electrochemical, optical, charge transport, and photovoltaic properties of these copolymers were examined. Compared to P1 with head‐to‐head coupling of two middle thiophenes, P2 with head‐to‐tail coupling of two middle thiophenes exhibits 40 nm red shift of absorption spectrum in film and 0.3 eV higher HOMO level. Both polymers exhibit field‐effect hole mobility as high as 0.02 cm² V^?1 s^?1. Polymer solar cells (PSCs) were fabricated based on the blend of the polymers and methanofullerene[6,6]‐phenyl C71‐butyric acid methyl ester (PC₇₁BM). The PSC based on P1 :PC₇₁BM (1:2, w/w) exhibits a power conversion efficiency of 2.7% under AM 1.5, 100 mW cm^?2, two times of that based on P2 :PC₇₁BM. The higher efficiency is attributed to lower HOMO (?5.6 eV) and smaller phase separation scale in P1 :PC₇₁BM blend. Tiny change in thiophene connection of P1 and P2 lead to great difference in HOMO, phase separation scale, and efficiency of their photovoltaic devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Polymerizable C70 derivatives with acrylate functionality for efficient and stable solar cells

Fullerene-based organic solar cells are generally suffering from severe microstructure evolution occurring in their bulk heterojunction active layers and thus are extremely stable. To address it, four polymerizable C₇₀ fullerene derivatives, [6,6]-phenyl-C₇₁-ethyl acrylate (PC₇₁EA), [6,6]-phenyl-C₇₁-propyl acrylate (PC₇₁PrA), [6,6]-phenyl-C₇₁-butyl acrylate (PC₇₁BA), and [6,6]-phenyl-C₇₁-pentyl acrylate (PC₇₁PeA), have been designed, synthesized, and investigated. These fullerene compounds have a molecular structure, shape and size very like the conventional C₇₀ fullerene acceptor, [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM), and have been found no different in their light absorption, redox potentials, and frontier orbital energy levels. Using these fullerene acrylates individually as acceptor and poly(3-hexylthiophene) as donor, organic solar cells have been fabricated and gave optimal efficiencies ranging from 3.32% to 4.16%, comparable to PC₇₁BM-based reference cells (4.06%). Owing to their acrylate functionality, these fullerene derivatives can turn into insoluble upon heating, and thus endow their solar cell devices much better thermostability than PC₇₁BM-based reference cells. The best one, coming from PC₇₁PeA devices, reported an optimal efficiency of 4.16%, and maintained 91.7% efficiency after heat treatment at 150 °C for 35 h. As a sharp contrast, the PC₇₁BM reference cell dropped its optimal efficiency from 4.06% to 0.48% only after 5 h heat treatment. X-ray diffraction, optical and atomic force microscopy, and space-charge-limited current method have been carried out to understand active layer structure, morphology, and charge mobility change during heat treatment.     

Diazaisoindigo bithiophene and terthiophene copolymers for application in field‐effect transistors and solar cells

Two donor–acceptor conjugated polymers with azaisoindigo as acceptor units and bithiophene and terthiophene as donor units have been synthesized by Stille polymerization. These two polymers have been successfully applied in field‐effect transistors and polymer solar cells. By changing the donor component of the conjugated polymer backbone from bithiophene to terthiophene, the density of thiophene in the backbone is increased, manifesting as a decrease in both ionization potential and in electron affinity. Therefore, the charge transport in field‐effect transistors switches from ambipolar to predominantly hole transport behavior. PAIIDTT exhibits hole mobility up to 0.40 cm²/Vs and electron mobility of 0.02 cm²/Vs, whereas PAIIDTTT exhibits hole mobility of 0.62 cm²/Vs. Polymer solar cells were fabricated based on these two polymers as donors with PC₆₁BM and PC₇₁BM as acceptor where PAIIDTT shows a modest efficiency of 2.57% with a very low energy loss of 0.55 eV, while PAIIDTTT shows a higher efficiency of 6.16% with a higher energy loss of 0.74 eV. Our results suggest that azaisoindgo is a useful building block for the development of efficient polymer solar cells with further improvement possibility by tuning the alternative units on the polymer backbone. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2691–2699     

Dithienosilole–phenylquinoxaline‐based copolymers with A‐D‐A‐D and A‐D structures for polymer solar cells

Two copolymers having D‐A‐D‐A ( P1 ) and D‐A ( P2 ) structures with quinoxaline acceptor unit and dithienosilole donor unit were synthesized and their optical and electrochemical (both experimental and theoretical) properties were investigated. The optical properties showed that these copolymers P1 and P2 exhibit optical bandgaps of 1.54 and 1.62 eV, respectively, with broader absorption profiles extending up to 800 nm and 770 nm, respectively. The electrochemical investigation of these two copolymers indicates that they exhibit suitable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels for efficient exciton dissociation and high open circuit voltage in the resultant polymer solar cells (PSCs). These copolymers were used as donors along with the PC₇₁BM as acceptor for the fabrication of solution processed bulk heterojunction PSCs. The optimized P1 :PC₇₁BM and P2 :PC₇₁BM active layers treated with solvent vapor treatment showed overall power conversion efficiency (PCE) of 7.16% and 6.57%, respectively. The higher PCE of P1 ‐based device as compared to P2 might be attributed to higher crystallinity of P1 and good hole mobility resulting more balanced charge transport. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 376–386     

Donor–acceptor photovoltaic polymers based on 1,4‐dithienyl‐2,5‐dialkoxybenzene with intramolecular noncovalent interactions

Donor–acceptor (D–A) conjugated polymers bearing non‐covalent configurationally locked backbones have a high potential to be good photovoltaic materials. Since 1,4‐dithienyl‐2,5‐dialkoxybenzene ( TBT ) is a typical moiety possessing intramolecular S…O interactions and thus a restricted planar configuration, it was used in this work as an electron‐donating unit to combine with the following electron‐accepting units: 3‐fluorothieno[3,4‐b]thiophene ( TFT ), thieno‐[3,4‐c]pyrrole‐4,6‐dione ( TPD ), and diketopyrrolopyrrole ( DPP ) for the construction of such D–A conjugated polymers. Therefore, the so‐designed three polymers, PTBTTFT , PTBTTPD , and PTBTDPP , were synthesized and investigated on their basic optoelectronic properties in detail. Moreover, using [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as acceptor material, polymer solar cells (PSCs) were fabricated for studying photovoltaic performances of these polymers. It was found that the optimized PTBTTPD cell gave the best performance with a power conversion efficiency (PCE) of 4.49%, while that of PTBTTFT displayed the poorest one (PCE = 1.96%). The good photovoltaic behaviors of PTBTTPD come from its lowest‐lying energy level of the highest occupied molecular orbital (HOMO) among the three polymers, and good hole mobility and favorable morphology for its PC₇₁BM‐blended film. Although PTBTDPP displayed the widest absorption spectrum, the largest hole mobility, and regular chain packing structure when blended with PC₇₁BM, its unmatched HOMO energy level and disfavored blend film morphology finally limited its solar cell performance to a moderate level (PCE: 3.91%). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 689–698     

Synthesis and investigation of photovoltaic properties for polymer semiconductors based on porphyrin compounds as light-harvesting units

We reported on two polymer semiconducting copolymers based on porphyrin compounds, poly[9,9-dioctylfluorene-co-5,15-bis(hexoxybenzyl)-10,20-bis(benzo-4-yl)porphyrin] (PFPor) and poly[9-(heptadecan-9-yl)carbazole-co-5,15-bis(hexoxybenzyl)-10,20-bis(benzo-4-yl)porphyrin] (PCPor), for use as organic photovoltaic materials. The thermal, optical, electrochemical, and photovoltaic properties of the two polymers were investigated. In addition, PC₆₁BM and PC₇₁BM were introduced as acceptor materials to confirm the acceptor effect in bulk heterojunction photovoltaic devices. Moreover, in order to establish acceptor effects, morphologies of polymer/PCBM blend films were analyzed through atomic force microscopy (AFM). PFPor and PCPor exhibited the best device performance with power conversion efficiencies (PCE) of 0.62% and 0.76%, respectively, upon the introduction of PC₇₁BM as the acceptor in the device where 86 wt.% of the PC₇₁BM was contained in the active layer (pol:PC₇₁BM = 1:6, w/w).